Process for the recovery of molybdenum



Patented Mar. 27, 1934 PROCESS FOR THE RECOVERY OF MOLYBDENUM Ernst Pokcrny, Leipzig, Germany, assignor to I. G;

Farbenindustrie Aktiengesellschaft, Frankforton-the-Main, Germany 1 No Drawing. Application April 9, 1931, Serial Nil.v 528,983. In Germany May 2, 1930 11 Claims.

The present invention relates to the recovery of molybdenum from mixtures of molybdenum or its compounds, with other substances.

This invention is an improvement of the proc- -:1 a ess forming the subject-matter of the application Seri No. 478,111, filed August 2'7, 1939, to Karl Winkler et al.,-according to which molybdenum is recovered practically completely from mixi tures of molybdenum or its compounds, with 1, 9; other metals, as for example chromium, zinc,

magnesium, and the like by subjecting the mixtures to a treatment with oxygen or gases containing or supplying oxygen, such as air, nitrogen oxides or the like at elevated temperatures not exceeding 609 C. and preferably below 500 0., but usually. not below about 400 C. No formation of any compounds between molybdic acid and other components of the mixture takes place, which could adversely affect the subsequent fur- Q. ther working up of the roasted material, when carrying out the recovery in the said manner. The said subsequent treatment, for the purpose of recovering the molybdenum, may be performed by treating the roasted material with .5. ammonia, and precipitating the molybdenum from the resulting ammoniacal solution under such conditions, as regards hydrogen-ion concentration, that complete separation of the molybdic acid from the other constituents is 139. obtained.

I have now found that the recovery of the molybdenum from the material roasted in the said manner is also advantageously effected by treating the latter with a solution of ammonium 35. sulphide, which may, if necessary, contain free ammonia. The extraction of the roasted material is preferably carried out in a vessel fitted with stirrers, in which case it is advisable to employ such an amount of ammonimn sulphide 4Q as will precipitate, in the form of sulphides, as

much as possible of the substances accompanying the molybdenum, without causing the for-- mation of more than a small quantity (if any) of ammonium sulphomolybdate. This amount 4. of ammonium sulphide is equivalent to the sulphide forming heavy metals other than molybdenum. If the amount of the sulphide-forming materials in the roasted charge is insufficient to combine With the whole of the sulphur liber- .5 9 ated in the formation of ammonium molybdate,

elements or compounds which will combine with the surplus sulphur present as sulphide ions to form insoluble sulphides are added either during or after the treatment with ammonium sulphide :5 solution, sinceit is generally desirable to prevent the formation of ammonium sulphomolybdate. The molybdenum, the whole of which is contained in the solution as ammonium molybdate, can be completely precipitated by acidification, for example with hydrochloric acid, the am moniaeal solution being preferably run into the acid. In so doing, it is important that a definite acidity which is generally smaller than n/ 1, and preferably n/ 1Q, should be maintained in order, on the one hand to prevent the precipitated molybdic acid from being partly redissolved, should the hydrogen-ion concentration be too high, and, on the other hand, contamination by other constituents in the event of said concentration being too low. 70

The advantages of extracting the roasted material withammonium sulphide as compared with the procedure specified in the aforesaid application Ser; No. 478,111 are due to the greater solvent properties of the said sulphide, so that the extraction maybe performed, for example even at ordinary temperature, and also to the smaller consumption of acid for precipitating the molybdic acid from the ammonium molybdate solution. A further advantage consists in that the precipitation of, the molybdic acid can also be performed at ordinarytemperature, because the substances forminginsoluble sulphides have already been eliminated in the extraction stage. i In treating, for example, a molybdenum-zinc catalyst employed in the pressure-hydrogenation process, the zinc sulphide-precipitated by the treatment with ammonium sulphide can be transformed into zinc oxide by. roasting, so that not only the molybdenu'rmbut also the zinc can be recovered, in a simple manner, in the original form present in the catalyst, whereas, in the method of operating according to the said application Ser. No. 478,111 the zinc is obtained as zinc chloride, the working up of which from the dilute solution is less economical.

The following examples will further illustrate the nature of this invention, but the invention is not restricted to these examples.

Example 1 A catalyst employed in the,pressure-hydrogen-. ation of organic substances, and consisting of molecular proportions of molybdenum, zinc and magnesium, in the form of their oxides or sulphides, is roasted with gases containing oxygen, in the manner'specified in Example 1 of the aforesaid application Ser. No. 478,111. The roasted material is then treated with a gradual addition of about 2 v litres per kilogram of a 10 per cent solution of ammonium sulphide containing about 2 per cent of free ammonia, in a vessel fitted with stirrers and at ordinary temperature, until the colour changes from light yellow to orange. Under these conditions the whole of the zinc is transformed, into 11150111? ble zinc/ sulphide, whereas molybdenum and magnesium pass into solution, the molybdenur'n being entirely in the form of ammonium molybdate, free from ammonium sulphomolybdate.

. After filtering 01f the insoluble zinc sulphide, the filtrate is treated, at ordinary temperature, with hydrochloric acid, in such an amount that the \liquid finally contains about 0.3 per cent of hydrogen chloride. Under this treatment the molybde :um is precipitated as molybdic acid, whilst th magnesium remains in solution as chloride.

1, Example 2 A mass iobtained by roasting a spent catalyst see Exam 1e 1) and consisting of about 80 parts of molybdi acid and 20 parts of zinc oxide, is treated 'wi about 2.4 litres per kilogram of 1 material 0 an ammoniacal liquor consisting of 0.7 use of 10 per cent aqueous ammonia and li.7 litres of 10 percent ammonium sulphide solution. The amountof sulphur present in the liquid is just suificient for the complete transformation of the zinc present into insoluble zinc sulphide; while the molybdic acid is transformed into soluble ammonium molybdate, without formation of ammonium sulphomolybdate. The molybdic acid can be recovered from the solution in the manner described in Example 1.

Example 3 A catalyst, roasted in the manner described in the said application Ser. No. 478,111, consisting of. 80 parts of molybdic acid, 20 parts of Zinc oxide and parts of magnesium oxide, is treated with an addition of a further 25 parts of zinc oxide, so as to attain the composition of the roasted material mentioned in Example 1. The further treatment is performed in the manner described in that example.

, The zinc sulphide obtained by filtering the reaction liquid is transformed into zinc oxide by roasting, and this product can then be employed in the treatment of further quantities of the specified catalyst material.

Example 4 A catalyst roasted in the manner described in the said application Ser. No. 478,111, consisting of parts of molybdic acid and 20 parts ofzinc oxide is treated with about 6.2 litres per kilogram of a 10 per cent ammonium sulphide solution (containing 2 per cent of free ammonia) that the whole of the Zinc is transformed into sulphide, and all the molybdenum present into ammonium sulphomolybdate.

The ammonium sulphomolybdate solution filtered off from the zinc sulphide is treated with sufiicient zinc oxide to extract the sulphur from the sulphomolybdate and form zinc sulphide (1.8

kilograms per each kilogram of roasted catalyst). The zinc sulphide formed is converted into zinc oxide by roasting.

i The zinc oxide may be replaced by some other compound furnishing an insoluble sulphide, such as cadmium oxide, lead oxide, stannous oxide or a mixture of several of such compounds.

Example 5 100 kilograms of a catalyst roasted in. the manner described in the said application Ser. No. 478,111, consisting of 90 parts of molybdic acid and 10 parts of chromic acid, are treated with 630 litres of a 20 per cent aqueous solution of ammonium sulphide containing 2 per cent of free ammonia, whereby practically the whole of the molybdic acid passed into solution as ammonium sulphomolybdate. The chromic acid remains behind undissolved. For the purpose of transforming the ammonium sulphomolybdate into ammonium molybdate, the filtered solution is treated with 560 kilograms of. lead oxide. The liquid is filtered and the molybdic acid is precipitated from the filtrate in the manner specified in Example 1. The filtration residue, consisting of lead sulphide, .is transformed, by roasting, into lead oxide which can then be employed in the treatment of a further quantity of the catalyst material.

What I claim is:

1. In the recovery of molybdenum from a material comprising molybdenum and at least one metal selected from the group consisting of mag nesium, zinc and chromium, the steps which comprise subjecting the said material to a treatment with a gas capable of liberating free oxygen at a roasting temperature not exceeding 600 C. and then converting the molybdenum oxides thus formed into soluble ammonium molybdate by treating the resulting mixture with so much of a solution of ammonium sulphide in the presence of a compound having a cation capable of forming an insoluble sulphide that no substantial quantity of ammonium sulfa-molybdate remains a after the conversion.

2. In the recovery of molybdenum from a material comprising molybdenum and at least one metal selected from the group consisting of magnesiumlzinc and chromium, the steps which comprise subjecting the said material to a treatment. with a gas capable of liberating free oxygen at a temperature between 400 and 600 C. and then converting the molybdenum oxides thus formed into soluble ammonium molybdate by treating the resulting mixture with a solution containing ammonia and so much ammonium sulphide in the presence of so much of a compound having a cation capable of forming an insoluble sulphide that no substantial quantity of ammonium sulfomolybdate remains after the conversion.

3. In the recovery of molybdenum from a material comprising molybdenum and at least one metal selected from the group consisting of magnesium, zinc and chromium, the steps which comprise subjecting the said material to a treatment with a gas capable of liberating free oxygen at a temperature between 400 and 600 0., treating the resulting mixture with a solution of ammonium sulphide and adding to this solution a substance combining with the sulphide ion to form an insoluble sulphide, the amount of ammonium sulphide and said substance being so coordinated as to preclude the formation of substantial quantities of ammonium sulfo-molybdate.

4. In the recovery of molybdenum from a material comprising molybdenum and. at least one metal selected from the group consisting of magnesium, zinc and chromium, the steps which comprise subjecting the said material to a treatment with a gas capable of liberating free oxygen at a temperature between 400 and 600 C. treating the resulting mixture with a solution containing free ammonia and ammonium sulphide and adding to this solution a substance combining with the sulphide ion to form an insoluble sulphide, the

ice

i-so

- oxygen at a temperature amount of ammonium sulphide and said substance being so coordinated. as to preclude the formation of substantial quantities of ammonium sulfo-molybdate.

5. In the recovery of molybdenum from a material comprising molybdenum and at least one metal selected from the group consisting of magnesium, zinc and chromium, the steps which comprise subjecting the said material to a treatment with a gas capable of liberating free oxygen at a temperature ranging from 400 to 500 C. then converting the molybdenum oxides thus formed into soluble ammonium molybdate by treating the resulting mixture with so much ammonium sulphide in the presence of so much of a compound having a cation capable of forming an insoluble sulphide that no substantial quantity of ammonium sulfo-molybdate remains after the conversion.

6. In the recovery of molybdenum from a material comprising molybdenum and at least one metal selected from the group consisting of magnesium, zinc and chromium, the steps which comprise subjecting the said material to a treatment with a gas capable of liberating free oxygen at a temperature ranging from 400 to 500 C., then converting the molybdenum oxides thus formed into soluble ammonium molybdate by treating the resulting mixture with a solution containing ammonia and so much ammonium sulphide in the presence of so much of a compound having a cation capable of forming an insoluble sulphide that no substantial quantity of ammonium sulfomolybdate remains after the conversion.

7. The process of recovering molybdenum from a mixture containing it and at least one metal selected from the class consisting of zinc, magnesium and chromium which comprises treating the mixture with a gas capable of liberating free ranging from 400 to 500 C. to effect a conversion of the metallic constituents of said mixture into the oxidic state, converting the oxides of molybdenum in said mixture into ammonium molybdate by adding ammonium sulphide to said mixture, the conversion being effected in the presence of a compound having a cation capable of combining with sulphur to produce an insoluble sulphide and with so much of the ammonium sulphide that no substantial quantity of ammonium sulfo-molybdate is formed, separating the ammonium molybdate from the reaction mixture and precipitating the oxides of molybdenum therefrom.

8. In the recovery of molybdenum from a material comprising molybdenum and at least one a metal selected from the group consisting of magtemperature between 400 and 600 nesium,'zinc and chromium, the steps which comprise subjecting the said material to a treatment with a gas capable of liberating free oxygen at a C., converting the molybdenum oxides thus formed into soluble ammonium molybdate by treating the resulting mixture with so much ammonium sulphide in the presence of so much of a compound having a cation capable of forming an insoluble sulphide that no substantial quantity of ammonium sulfomolybdate remains after the conversion and acidifying the ammonium molybdate to precipitate molybdic acid therefrom.

9. The process of recovering molybdenum from a mixture containing it and at least one metal selected from the class consisting of zinc, magnesium and chromium which comprises treating the mixture with a gas capable of liberating free oxygen at a temperature ranging from 400 to 500 C. to effect a conversion of the metallic constituents of said mixture into the oxidic state, converting the oxides of molybdenum in said mixture into ammonium molybdate by adding ammonium sulphide to said mixture, the conversion being effected in the presence of a compound having a cation capable of combining with sulphur to produce an insoluble sulphide and with so much of the ammonium sulphide that no substantial quantity of ammonium sulfomolybdate is formed, separating the ammonium molybdate from the reaction mixture and adding thereto hydrochloric acid to precipitate molybdic acid therefrom.

10. In the recovery of molybdenum from a spent catalyst employed in the destructive hydrogenation of carbonaceous materials and which consists of about molecular proportions of molybdenum, zinc and magnesium in the form of their compounds with at least one of the first two elements of the sixth group of the periodic system, the steps which comprise subjecting said catalyst to careful roasting at from 460 to 480 C. and treating the resulting mixture with a gradual addition of a 10 per cent solution of ammonium sulphide containing about 2 per cent of free ammonia until the color changes from light yellow to orange.

11. In the recovery of molybdenum from a spent catalyst employed in the destructive hydrogenation of organic substances and which consists of about 0.? molecular proportion of molybdenum and about 0.3 molecular proportion of zinc in the form of their compounds with at least one of the first two elements of the sixth group of the periodic system, the steps which 

